Any Railroad Savvy People Out There?

I have been searching for years now for more information on my greatgrandfather's accident while he was an 'engineer for the Northern Pacific on a western division' (according to his obituary) or, while working for Chicago Northwestern as a brakeman (according to a family member)Clayton Dick Herbert lost his leg in a railway accident ... that much I am certain of. I'm assuming this happened between 1870 and 1880 but am not positive of that. I'm basing my assumption on finding him as a day labourer in 1870 on his Father's farm in Iowa and, in June of 1880, as a restaurant owner in the Dakota Territory. He and my greatgrandmother were married in April of that year. He was a restauranter/saloon keeper/lunchroom owner for the remainder of his life. What I'm trying to find is where and when he was actually injured. I thought the railroads would have records of serious accidents like his but I can't even find sites that tell me who to ask. I did try contacting a few that I found online but never received a reply.

So, any hints any of you have would be greatly appreciated! Thanks!